In vitro fertilization and risk of childhood leukemia in Greece and Sweden.

Cancer risk in children born after in vitro fertilization (IVF) remains largely unknown. We aimed to investigate risk of leukemia and lymphoma following IVF using two nationwide datasets. The hospital-based case-control study in Greece derived from the National Registry for Childhood Hematological Malignancies (1996-2008, 814 leukemia and 277 lymphoma incident cases with their 1:1 matched controls). The Swedish case-control study was nested in the Swedish Medical Birth Register (MBR) (1995-2007, 520 leukemia and 71 lymphoma cases with their 5,200 and 710 matched controls) with ascertainment of incident cancer cases in the National Cancer Register. Study-specific and combined odds ratios (OR) were estimated using conditional logistic regression, with adjustment for possible risk factors. Nationwide studies pointed to similar size excess risk of leukemia following IVF, but to a null association between IVF and lymphoma. The proportion of leukemia cases conceived through IVF was 3% in Greece and 2.7% in Sweden; prevalence of IVF in matched controls was 1.8% and 1.6%, respectively. In combined multivariable analyses, the increased risk of leukemia was confined to age below 3.8 years (OR = 2.21; 95% confidence interval, CI: 1.27-3.85) and to acute lymphoblastic leukemia (ALL) (OR = 1.77; 95% CI: 1.06-2.95) with no sufficient evidence of excess risk for other leukemias (OR = 1.34; 95% CI: 0.38-4.69). Following IVF, OR for ALL was 2.58 (95% CI: 1.37-4.84) before age 3.8 and 4.29 (95% CI: 1.49-12.37) before age 2 years. IVF seems to be associated with increased risk of early onset ALL in the offspring.